Irritable bowel syndrome (IBS) or spastic colon is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, a low-grade gut inflammation was reported. Diarrhoea or constipation may predominate, or they may alternate (classified as IBS-D, IBS-C respectively). IBS may begin after an infection (post-infectious, IBS-PI), a stressful life event or onset of maturity without any other medical indicators. In IBS, routine clinical tests yield no abnormalities, though the bowels may be more sensitive to certain stimuli, such as balloon insufflation testing.
IBS is a very common condition affecting approximately 15% of the population at any one time. There are about twice as many women as men with this condition. IBS is a source of chronic pain, fatigue and other symptoms, and it increases a patient's medical costs, and contributes to work absenteism. Researchers have reported that the high prevalence of IBS, in conjunction with increased costs produces a disease with a high societal cost. It is also regarded as a chronic illness and can dramatically affect the quality of a sufferer's life.
A leading theory about the cause of IBS relates to the enteric nervous system (ENS). The enteric nervous system (ENS) is a subdivision of the peripheral nervous system (PNS) that directly controls gastro-intestinal (GI) functions and is embedded in the lining of the gastrointestinal system. It includes efferent neurons, afferent neurons, and interneurons. The structural and physiological functioning of the ENS is performed by glial cells (astrocytes). The ENS is organized into two major plexus with functional specific roles.
The myenteric plexus, located between the longitudinal and circular muscle, contains neurones mainly involved in the control of intestinal motility. Through intestinal muscles, the efferent or motor neurons control peristalsis and churning of intestinal contents. The motor neurons controlling motility are composed of two major classes:                excitatory myenteric neurons liberating acetylcholine (referred to as Choline AcetylTransferase ImmunoReactive neurons (“ChAT-IR” or “ChAT” or “ChAT neurones” or “ChAT nerves”) and/or substance P (SP) for contractions, and        inhibitory myenteric neurons liberating nitric oxide (identified as Nitric Oxide Synthase neurons (NOS-IR)) and/or Vaso-active Intestinal Peptide (VIP) for relaxation.        
Choline acetyltransferase EC 2.3.1.6 is an enzyme that is synthesized within the body of a neuron and transferred to the nerve terminal. The role of ChAT is to join Acetyl-CoA to choline, resulting in the formation of the neurotransmitter acetylcholine. Experimentally, effect on acetylcholine production is extrapolated from the determination of the number of ChAT neurons, typically an increase in the number of ChAT nerves is indicative of an increase of acetylcholine.
The submucosal plexus, located between the circular muscle and the mucosa, contains neurons mainly involved in the control of intestinal epithelial barrier (IEB) functions, such as paracellular permeability. In particular, activation of enteric neurones in the submucosal plexus decreases paracellular permeability, via the liberation of VIP, whereas acetylcholine (Ach) increases paracellular permeability, setting the basis of a fine ‘tuning’ of the IEB permeability by the ENS. Thus, concerning the neuronal control of paracellular permeability, the increase of VIP liberation by submucosal neurons increases IEB integrity while the increase of submucosal plexus ChAT neurons decreases IEB resistance.
Although there is at current no cure for IBS, there are treatments which attempt to relieve symptoms, including dietary adjustments, medication and psychological interventions.
Probiotics, in particular strains of lactic acid bacteria, are reported to be beneficial in the treatment and/or prevention of IBS. Examples of such disclosures are WO 2007/036230, WO 03/010297, and WO 2009/080800. However, the bacterial strains are selected for their effect on the immune system, on intestinal permeability or on the intestinal microbiota and not for their effect on improving the function of the ENS. WO 2008/064489 discloses the use of probiotics to block an intermediate conductance calcium dependent potassium current resulting in an anti-inflammatory effect. WO 2007/132359 discloses the use of Lactobacillus and a cannabinoid receptor agonist and/or an opioid receptor antagonist in relation to pain perception. WO 2006/032542 discloses the use of Lactobacillus for analgesic purposes. Kamm et al, 2004, Neurogastrointest. Motil 16: 53-60 disclosed effects of S. boulardii on decreasing calbindin-28 k (CALB) but not on other neuronal markers of the pig jejunum. Metugriachuk et al, 2006, Rejuvenation Res. 9: 342-345 disclose that a symbiotic preparation on motility of small and large intestine in old Wistar rats significantly increased the myoelectric activity of small intestine and colon, an increased mRNA expression of VIP, but no significant effect on VIP concentration.
Further research is therefore needed on individual strains of probiotic bacteria with a beneficial effect on the ENS for use in IBS, constipation and/or other disorders.